1. Field of the Invention
The present invention relates to optical transmitting elements having their respective configurations in compliance with various purposes respectively and, more particularly, to a resinous optical transmitting element which is low in transmission loss and suitable for communication over short distances and to a method of manufacturing the optical transmitting element.
2. Description of the Prior Art
As disclosed, for example, in Japanese Patent Application Laid-Open Nos. 61-26012 and 61-14607, a conventional optical transmitting element is processed into a curled configuration or the like after the element has been molded. Further, in an optical transmitting element disclosed in Japanese Patent Application Laid-Open No. 57-45502, a cladding lower in refractive index than a core through which light is transmitted, is formed into a tube, and core material is poured into the tube. The poured core material is polymerized so that the core and the cladding are united to each other, to form an optical transmitting element.
In the prior art described above, no consideration is made to a distortion within the optical transmitting element, which occurs due to post-processing of the optical transmitting element. By this reason, there arise such problems that the distortion causes the transmission loss to increase, and the surface roughness of an interface between the core and the cladding is coarse thereby making it impossible to reduce the transmission loss.
Moreover, in a method of obtaining an optical transmitting element by means of cast molding, a tube is utilized, as it is, as a cladding. According to this method, the cladding material employs fluoric resin because the cladding material is required to have a low refractive index. Since, however, the fluoric resin is high in molding temperature and is inferior in moldability, there arises such a problem that it is impossible for the fluoric resin to mold articles complicated in configuration. Furthermore, in the method in which the tube is molded and the core material is put into the tube and is polymerized, the transmission loss occurs because of the surface roughness of the inner surface of the tube. Further, in the prior art method, no consideration is made to molding of a graded-index (GI type) in which the refractive index of the optical transmitting section, i.e., the core is in the form of a quadratic distribution.